Datasheet

STLDC08 Application information
Doc ID 18476 Rev 1 19/29
Equation 11
Equation 12
Equation 13
If the R
DS (ON)
of the main Power MOSFET is used to sense the current on the inductor the
following procedure must be performed to choose the Power MOSFET. During ON time, the
SENSE comparator limits the voltage across the Power MOSFET to a nominal 100 mV. In
that case, the maximum inductor current is given by the following relationships:
Equation 14
Equation 15
Equation 16
8.5 Power MOSFET selection
A key parameter to take into account in the selection of the N-MOSFET is the maximum
continuous drain current. As a safety design, it is important to choose a maximum
continuous drain current equal to twice the maximum input current.
)PK(L)MAX(IN
I2I ×=
2
I
D1
I
I
L
MAX
LED
)PK(L
Δ
+
−
=
)PK(L
SENSE
I2
1.0
R
×
=
)ON(DS)ON(DS
SENSE
)MAX(L
R
mV100
R
V
I ==
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
Δ
+×
−
×=×=
2
I
1
D1
I
2I2I
L
MAX
LED
)PK(L)MAX(L
⎟
⎠
⎞
⎜
⎝
⎛
Δ
+××
−
×<
2
I
1I2
D1
1.0R
L
LED
MAX
)ON(DS